The invention relates to molecular, inorganic glasses composed, at least in part, of one species including either thermally stable (i.e., persisting after annealing), zero-dimensional molecules or network-forming groups, composed of arsenic and sulfur atoms and associated with germanium atoms.
The physical structure of a glass may be characterized by its dimensionality, that is, by the number of directions in which its components extend. Thus, vitreous selenium, which is believed to consist of intertwined chains of selenium atoms, is said to have a one-dimensional structure. Likewise, glassy As2S3, which consists of corrugated sheets of As2S3 pyramids that share corners, is described as having a two-dimensional structure. Considered in these structural terms, most oxide glasses are said to be three-dimensional.
A certain class of crystalline, inorganic compounds, known as molecular solids, has a zero-dimensional structure. This structure consists of molecular clusters in a cage-like form. As such, the clusters are repeated periodically in three dimensions, but are only bonded to each adjacent cluster by van der Waals forces. Examples of crystalline, inorganic compounds that have such a structure are known. They include arsenic sulfide, which consists of eight atom clusters designated As4S4, and phosphorus sulfide, which consists of 14 atom clusters designated as P4S10.
The possibility of an inorganic glass having such a structure has been suggested by R. Zallen. Zallen has suggested that such a zero-dimensional structure may occur temporarily in amorphous arsenic sulfide films which have been fabricated by vapor-phase deposition. Although such structure is found in these films initially upon cooling, it is thermally unstable in that it is lost upon annealing the films.
The present invention is based on a discovery that bulk, inorganic glasses can be produced, which consist almost entirely of thermally-stable, zero-dimensional clusters. These novel glasses have some physical properties similar to those observed in organic plastics. The glasses, however, also exhibit other properties that more closely resemble those found in conventional, three-dimensional, inorganic glasses such as complete transparency between the visible and infrared cutoff wavelengths. Unlike plastics, the present glasses are also essentially impermeable to gases and moisture. Hence, for instance, these glasses may be useful as low-temperature, hermetic, sealing materials in various industrial applications.
The invention resides, in part, in an inorganic glass that is resistant to devitrification. At least about 95% of the glass composition, in atomic percent, comprises about: 42-60% arsenic (As), up to 48% sulfur (S), 0-14% selenium (Se), or optionally, up to about 12% germanium (Ge); and comprising, in substantial part, at least one species including either thermally stable (i.e., persisting after annealing), zero-dimensional molecules or network-forming groups. Preferably, the glass has 37-48% sulfur, or the content of S+Se is about 37-48%. As used herein, the term xe2x80x9catomic percentxe2x80x9d refers to the actual percent of the total number of atoms present in a composition. Thus, the value given for a particular element represents the percent of atoms of that element present in a composition relative to 100 percent for the total number of atoms in the composition.
According to an embodiment, at least a portion of the zero-dimensional molecules or clusters has a composition comprising either four atoms of arsenic and three atoms of sulfur (As4S3), or four atoms each of arsenic and sulfur (As4S4). The zero-dimensional molecular clusters are bonded to each other primarily by van der Waals forces. Alternatively, at least a portion of the network-forming groups comprise a variety of species, expressed in terms of Asxe2x80x94(S, As)n units, wherein nxe2x89xa0zero. Examples may include either AsS3 (AsS3/2, wherein the S atoms are shared with other adjacent As atoms), AsAsS2, AsSAs2, or AsAs3.
The invention further resides in a method of producing a thermally-stable, Asxe2x80x94S glass that is composed, in part at least, of zero-dimensional clusters composed of four atoms of arsenic and three atoms of sulfur, or four atoms each of arsenic and sulfur. The method comprises forming a mixture of 42-60% arsenic, 37-48% S+Se, wherein the Se is 0-14%, with, optionally, up to 12% germanium (Ge), and melting the mixture to form a devitrification-resistant, inorganic glass melt.
Additional features and advantages of the present method and array device will be disclosed in the following detailed description. It is understood that both the foregoing summary and the following detailed description and examples are merely representative of the invention, and are intended to provide an overview for understanding the invention as claimed.